Hitherto, functional layers made of various functional materials are produced by the physical vapor deposition method (PVD) such as vacuum vapor deposition, laser ablation, sputtering, or ion plating, or by the chemical vapor deposition method (CVD) such as heat CVD, light CVD, or plasma CVD. These generally require a large-scale apparatus, and among these, some are not suited for forming a layer of large area.
For example, with respect to a transparent conductive layer, the following description can be made. At present, the transparent conductive layer is produced mainly by the sputtering method. There are various modes for the sputtering method, for example, a method of forming a layer by allowing inert gas ions, which are generated by direct current or high-frequency discharge, to be accelerated to hit the surface of a target in vacuum so as to strike out atoms constituting the target from the surface for deposition on the substrate surface.
The sputtering method is excellent in that a conductive layer having a low surface electric resistance can be formed even if it has a large area to some extent. However, it has a disadvantage that the apparatus is large, and the layer forming speed is slow. If the conductive layer is to have a still larger area from now on, the apparatus will be further enlarged. This raises a technical problem such that the controlling precision must be heightened and, from another point of view, raises a problem of increase in the production cost. Further, although the number of targets is increased to raise the speed in order to compensate for the slowness of the layer forming speed, this also is a factor that enlarges the apparatus, thereby raising a problem.
An attempt is made to produce the transparent conductive layer by the application method. In a conventional application method, a conductive paint having conductive fine particles dispersed in a binder solution is applied onto a substrate, dried, and hardened to form the conductive layer. The application method has advantages in that a conductive layer having a large area can be easily formed, that the apparatus is simple and has a high productivity, and that the conductive layer can be produced at a lower cost than by the sputtering method. In the application method, an electric path is formed by contact of the conductive fine particles with each other, whereby the electric conductivity is exhibited. However, the conductive layer produced by the conventional application method has an insufficient contact, and the obtained conductive layer has a high electric resistance value (i.e. is inferior in conductivity), thereby limiting its usage.
As an application method using no binder resin, for example, Japanese Laid-open Patent Publication No. 8-199096 (1996) discloses a method in which a conductive layer forming paint comprising tin-doped indium oxide (ITO) powders, a solvent, a coupling agent and an organic or inorganic acid salt of metal, and not containing a binder is applied onto a glass plate and calcined at a temperature of 300° C. or higher. In this method, since the binder is not used, the conductive layer has a low electric resistance value.
Also, a process is known in which a layer is formed by application using the sol-gel method. An application method using the sol-gel method is suited for forming a layer of large area.
By any of the above-mentioned application methods, in the case that the support is one having flexibility such as a film, a functional layer having a large area can be easily formed, however, in the case that the support is one having poor flexibility such as a plate material, the application is difficult as compared with the case of the flexible support, and particularly it is difficult to control a layer thickness for uniformity. Namely, in the case of the flexible film, the application can be performed by fixing a coater section and moving the film, thereby easily controlling a layer thickness. On the other hand, in the case of the plate material having poor flexibility, although the application can be performed by moving the plate material if the application area is small, accuracy of the layer thickness is liable to deteriorate due to wobbling or others by moving the plate material if the application area is large. Also, although a method moving the coater section may be mentioned, accuracy of the layer thickness deteriorates if flatness of the plate material is poor.
Also, Japanese Laid-open Patent Publication No. 6-103839 (1994) discloses a method for manufacturing a transparent conductive substrate by transferring.